If this is factory installed (most likely not) then you would have a fuse in a 12V fuse box. Since it's my guess that it's not factory, then I would suggest you remove the wall plate switch and trace the 12V wire back to the source of the 12V power. It's most likely tapped into your OTA TV antenna power or a similar source near the plate.
What I post is my 2 cents and nothing more. Please don't read anything into my post that's not there. If you disagree, that's OK.
Can't we all just get along?